With ever increasing volumes of road traffic, improvements in the performance of traffic signal control systems can be a cost-effective way to potentially reduce social, economic and environmental impacts, which arise from traffic congestion. Such improvements may not only delay the onset of traffic congestion but can also avoid expensive and time consuming additions to road network infrastructure.
Many traffic control systems in use around the world are time-based and use switching plans developed manually by collecting traffic patterns for each time of the day. These plans are fixed and do not respond at all to unexpected real time changes in traffic flow.
Traditionally, traffic control systems are equipped with adaptive fixed phase controllers where traffic lights are usually switched in a sequence through several repeating phases. Conventional traffic control systems cannot provide adequate utilisation of controlled intersections. As a result, there is usually a long average waiting time for vehicles to cross intersections that are controlled by conventional traffic control systems.
Adaptive control systems such as SCOOT (Split Cycle Offset Optimization Technique) and SCATS (Sydney Coordinated Adaptive Traffic System), were first developed a few decades ago and they use adaptive phase control where the lights are switched through several phases in a cyclic sequence. Traffic engineers manually select the phases and predefine their ordering. The systems make real time adjustments in the time between each phase. The real time adjustments are based on the measurements of the traffic flow saturation levels.
However, these adaptive phase systems are still not capable of adapting to unanticipated flow patterns. None of the previously devised adaptive control systems can provide a greater degree of flexibility than controlling individual signal groups. The known adaptive control systems demonstrate significant drawbacks when unplanned traffic flow conditions are encountered. This is because these existing adaptive controllers are limited to switching between a limited number of phases in a predetermined order.
Moreover, historically the controlling methodologies that are applied in conventional traffic controlled systems employed a different way to estimate the end-of-queue time and green light time. Previously, for example, gap detection has been used to help switch traffic lights and SCATS balanced the degree of saturation (DoS) at a target DoS to update green light time for phases. These techniques are sensitive to variations, and are unable to allow the system to respond quickly to high rates of traffic flow changes.
It would therefore be an advantage to deliver a solution that works optimally for controlling traffic lights at intersections, which is able to plan a control policy for a high dimensional complex, probabilistic, non-linear system, subject to signal switching constraints and traffic behaviour.
It would also be advantageous to provide an improved method and system for controlling traffic lights at intersections. This would overcome at least some of the disadvantages of previously known approaches in this field, or would provide a useful alternative.